1. Field of the Invention
This invention generally relates to impact and thermal distortion resistant thermoplastic resin compositions, and more particularly relates to impact-modified polyvinyl chloride/polycarbonate alloy compositions.
2. Description of the Prior Art
Polyvinylchloride (PVC) is a high volume, relatively inexpensive polymer. However, the use of PVC is often limited because it lacks properties required for many service applications. Efforts to develop PVC blends or alloys with other materials which meet the demands of commercial service applications have therefore continued.
For example, PVC alone lacks the dimensional stability under heat required for many service applications. To address this problem, it is known to alloy PVC with polycarbonate to form an alloy composition having dimensional stability under heat surpassing that of PVC alone. For example, Abdrakhmanova et al., SU 84-3788283, 31 Aug. 1984, describe a mixture of 100 parts polyvinyl chloride and 1-8 parts oligomeric bisphenol A polycarbonate. PVC/polycarbonate alloys, however, often lack acceptable impact strength. Efforts have therefore been made to discover impact modifiers that can be added to PVC/polycarbonate alloys to make an overall composition having both acceptable impact strength and dimensional stability under heat.
In this connection, U.S. Pat. No. 3,882,192 issued to Elghani et al. in 1975 describes molding compositions consisting of 5-95 parts by weight of a polycarbonate, 5-95 parts by weight of a vinyl chloride polymer, and 5-95 parts by weight of an acrylonitrile butadiene styrene copolymer or a styrene/maleic anhydride copolymer or an ethylene-vinyl acetate copolymer.
On the other hand, U.S. Pat. No. 4,680,343 issued to Lee in 1987 describes chlorinated polyvinyl chloride (CPVC) alloys containing aromatic polycarbonates, ethylene-based functional polymers and optionally an impact modifier. The Lee patent notes that CPVC and PVC are different materials and that PVC prior art is not analogous to patentability issues relating to CPVC since PVC processes easily and CPVC does not, since CPVC has heat resistance but PVC does not, and furthermore, since CPVC has a high melt viscosity but PVC does not.
Despite these and other efforts, the need continues for PVC/polycarbonate alloy compositions having high impact properties. Efforts to find such compositions have been frustrated because the effects of differing impact modifiers on PVC/polycarbonate blends vary greatly, and it is thus difficult to discover impact modifiers which provide overall alloys having high impact and other desirable properties.
The applicant's invention now addresses this need and provides impact and thermal distortion resistant PVC alloys having other advantageous properties as well.